1. Field of the Invention
The present invention relates generally to electrical power production, and more specifically to a small gas turbine engine driving a number of small generators.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Electric power is produced in a large power plant using a large industrial gas turbine engine to drive a large electric generator to produce power in the megawatt and higher range. This type of electric power plant is good for providing electricity to a large number of houses but not practicable for small scale use. In some situations, a small electric generator is required to provide electrical power to a single user in the range of less than one megawatt. Diesel engines are used to drive a standby electrical generator to provide power in the case of an emergency, for example, to a hospital or a grocery store when the main source of power has been interrupted.
Because of the recent increase in the price of fuel, diesel engines are beginning to be replaced by small gas turbine engines. A gas turbine engine has about twice the efficiency of the diesel engine. However, a small gas turbine engine rotates at very high speeds compared to a diesel engine. For this reason, a typical electric generator requires a reduction gear box to step down the rotation speed from the engine to the generator in order to meet the generator speed rating. The addition of a reduction gear box not only requires oil for lubrication but also reduces the overall efficiency of the power plant because of the loss through the gears.
Small electric generator of the 400 kW range that operates at very high speeds (greater than 3,600 rpm) is known in the art of electric generators. Regular generators operate at 3,600 rpm in order to produce 60 hertz electrical current without the need of a reduction gear box. These high speed generators are used with a direct drive that eliminates the need for a gearbox and oil lubrication system. These high speed generators uses efficient permanent magnet motor/generator in which the generator can also operate as a motor. Because of the type of magnet used, the generator/motor can be used in close proximity to a high temperature device, thus making these high speed generators ideal for use with a small gas turbine engine for electric power production. Also, these prior art generators are designed to operate at a certain high speed in order to generate the maximum amount of electric power. Some high speed generator/motors might be designed to produce 200 kW while others might be designed to pro duce 300 kW or 400 kW of electric power and all are designed to operate at the same high rotation speed.
The high speed generators are a complex machine designed for a specific power level such as in the 400 kW range. The problem is, when higher power is required, a new generator must be designed for this higher power output. For example, when the situation requires 600 kW, the 400 kW generator is not large enough. Therefore, a new design of the generator is required in which 600 kW will be delivered. This is very costly and time consuming.
Also, a compressor can be driven by an electric motor to produce compressed gas. And, a turbine can drive an electric generator to produce electric power. In each of these cases, the compressor and the turbine requires a thrust bearing assembly to counteract the resulting axial force developed from the compression or the expansion of the gas. The prior art high speed motor/generator unit described above includes a magnetic bearing assembly for dynamic force compensation, flux command, inertial balance and magnetic balance.
U.S. Pat. No. 1,066,209 issued to Ljungstrom on Jul. 1, 1913 and entitled TURBINE GENERATOR shows a steam turbine connected to two electric generators located on the ends of the turbine that provide support for the turbine. U.S. Pat. No. 4,616,140 issued to Bratt on Oct. 7, 1986 and entitled SYSTEM AND A METHOD FOR CONVERSION OF SOLAR RADIATION INTO ELECTRIC POWER shows a solar collector mirror with a hot gas engine driven by heat reflected off of the mirror and two generators connected on the ends of the engine. U.S. Pat. No. 2,110,142 issued to Wilkinson on Mar. 8, 1938 and entitled POWER TRANSMISSION SYSTEM FOR WELL DRILLING AND THE LIKE shows a prime mover connected to two generators on each side to produce electric power. In each of the above inventions, the generator is not designed to be easily fitted to the driving motor and the generator does not have the capability to connect to an additional generator on the side opposite to the driving motor.